418 Dr. H. J. Hansen on the Morphology of the 
with a large number of the animals, as also with the investi- 
gations and opinions of the anatomists, embryologists, and 
systematists with reference to the main details of the morpho- 
logy and classification of the forms with which we are con- 
cerned. ‘The greater part of these investigations have been 
carried out with the aid of the dissecting-microscope, often 
with a magnifying-power of one hundred diameters. My 
experiments show that it is often possible to study the articu- 
lation and composition of the mouth-parts much better with 
this instrument than by means of higher magnification under 
the compound microscope ; the latter, however, is much more 
frequently employed. A reagent of which I have very often 
availed myself is a strong cold solution of caustic potash, in 
which the preparations are placed until the internal tissue is 
partially or completely decomposed and can be washed away 
in glycerine. I have frequently found it very advantageous 
to use specimens which had lain for a very long time in spirit 
so weak that the muscles and the connective tissue could be 
removed fairly easily by preparation, whereby I avoided the 
effect of the potash in making the thin chitin too transparent. 
These observations are here made in case any one should 
wish to test or dispute my results, while at the same time I 
emphatically urge those who are interested in the subject to 
investigate in the manner indicated a larger series of forms 
belonging to several orders. Inducements for a test may 
possibly be afforded by my chief results, which are as 
follows :—The demonstration of three segments in the axis 
of the appendages of Crustacea as the primitive and still 
frequently existing condition; the division of the Malaco- 
straca, based inter alia upon the different structure of the 
thoracic limbs; the demonstration of the existence in the 
case of Thysanura and certain Orthoptera of four pairs of 
mouth-parts, with which those of the Amphipoda are homo- 
logous ; and the proof of a much greater agreement between 
the head of a Machilis and that of the malacostracous 
Crustacea than was hitherto assumed to be the case. 
It would lead us too far afield to quote (not to speak of 
discussing) the enormous literature which belongs to the 
questions here indicated. Only once or twice do [| refer to 
an author more precisely, when I have not found an oppor- 
tunity of closely investigating the forms which are the 
subjects of his statements or am entirely ignorant of them ; 
when, as most frequently happens, I content myself with 
giving the name of an author in parenthesis, it signifies that 
the writer in question has expressed the same opinion before 
me (thus affording a confirmation of my statement), but that I 
